Swing-rotor-type centrifugal separators, which are used for conducting a test on blood or urine and rotate a sample container accommodated in a bucket capable of swinging, have been used. Many swing-rotor-type centrifugal separators have maximum rotation speeds of about 3000 rpm to 5000 rpm. A swing rotor has a hub extending coaxially with a drive shaft disposed in a centrifugal chamber, a rotor body disposed around the hub, and a plurality of arms extending from the rotor body. As for the arms, a plurality of pairs of arms are provided, arms of each pair face each other, and each pair of arms supports a bucket for holding a sample container such that the bucket is rotatable. There are various kinds of swing rotors. In general, holding pins are formed at the arms of a swing rotor, pin receiving portions are formed at both sides of each of the buckets for accommodating samples, and the buckets are held to the holding pins by the pin receiving portions. The holding pins are often disposed to be aligned with a swing center axis, and are fixed on the swing rotor side. However, the holding pins may be formed on the bucket side.
If the swing rotor rotates in the centrifugal chamber, each bucket supported or hooked by each pair of holding pins provided to the arms swings in a horizontal direction around the corresponding pair of holding pins by a centrifugal force, such that centrifugal separation of a sample in a sample container is performed. During a centrifugal separation operation, it is required to stably hold the sample container in a constant posture. For this reason, it is general to accommodate a plurality of sample containers in a dedicated rack and load the rack in a bucket.
The dedicated rack is designed according to an internal shape of a bucket to be loaded thereon, and is manufactured by using, for example, polypropylene or polyacetal resin. Further, the rack is configured to have a plurality of insertion holes with one end enclosed, according to the kind of sample containers to be accommodated therein. For example, plastic or glass test tubes are generally used as sample containers used for a test on blood or urine, and a rack is formed in a shape capable of vertically disposing the sample containers at even intervals. Volumes of samples contained in the sample containers such as test tubes are often uneven, and thus there may be a variation in a center of gravity of the rack in which the sample containers has been set. Particularly, in a case of sample containers called vacuum blood-collecting vessels used for blood tests, a difference in mass between the sample containers easily occurs due to a difference in blood quantity or a difference in specific gravity of blood.
For this reason, when the sample containers are accommodated in the dedicated rack, it is important to confirm a mass of each sample container so as to check whether a total mass of the sample containers to be accommodated in each rack is within an allowable value range and to confirm whether a mass difference between racks loaded at rotation positions facing the rotation axis of the swing rotor is within an allowable value range of the centrifugal separator. Also, it is important to adjust alignment of sample containers such that the center position when the swing rotor is seen from the above are aligned with the center axis lines of holding pins at the greatest extent.
In general, in an automatic centrifugal apparatus which automatically carries sample containers in and out, it is relatively easy to adjust a total mass in a dedicated rack or a mass difference between racks facing each other. However, in a case where a dedicated rack, in which a plurality of sample containers is accommodated manually, it is very difficult to dispose the sample containers in consideration of the center of gravity of the rack. For this reason, in order to prevent sample containers from being randomly accommodated in the rack, for example, the order or positions of the sample containers to be accommodated in the rack has been designated. However, even if the order or positions are designated, the center of gravity of the bucket may not be aligned with the center axis lines of the holding pins, and in some cases, the bucket may rotate in an inclined state (a state in which the center of gravity is different from an ideal position).
Further, sliding based on contact by the holding pins and the pin receiving portions of the bucket is required in a swing rotor, and in a case where the rotation of the swing rotor stops, the bucket is required to accurately return to an original position. However, in a case where influence of friction is great, the bucket may not smoothly swing, and in the worst case, the bucket may stop in the middle. Particularly, in a centrifugal apparatus which automatically carries sample containers in and out, if a bucket does not return to an original position after swinging, not only a problem may occur when carrying the sample containers in and out but also the samples may be damaged. In order to solve these problems, it is necessary to frequently apply lubricant grease on the holding pins so as to reduce friction. However, in an automatic centrifugal apparatus which is required to be continuously operated, frequent grease application increases the maintenance time of the apparatus, and is cumbersome. For this reason, users demand that this maintenance interval should be made further longer.
A countermeasure technology for these problems is disclosed in related-art. In related-art, a front edge of a holding pin, which is provided at a front edge of each arm, has a tempered shape in which the front edge widens radially, and the holding pin is disposed in a normal direction, such that the holding pin is brought into point contact with a pin receiving portion of a bucket so as to reduce sliding resistance.
In a rotor for a centrifugal separator disclosed in related-art, the sliding resistance of the holding pin is reduced. However, since the holding pin is in almost point contact with the pin receiving portion during a centrifugal separation operation, a local surface pressure becomes high. Therefore, in a case where it is desired to increase the mass of the bucket, it is difficult to secure a sufficient strength. Further, in a case of a bucket which accommodates a plurality of sample containers, a bucket may be held in an inclined state according to a center of gravity during a centrifugal separation operation, such that the position of the contact area (almost point contact) between the holding pin and the pin receiving portion of the bucket becomes unstable.
The present invention was made considering the above-mentioned circumferences, and an object of the present invention is to provide a swing rotor for a centrifugal separator and a centrifugal separator which suppress sliding resistance during swinging of a bucket, so as to prevent defect in swing.
Another object of the present invention is to provide a swing rotor for a centrifugal separator and a centrifugal separator which are capable of stably maintaining a swing state during a centrifugal separation operation even when a slight variation occurs in a center of gravity of a bucket.
Another object of the present invention is to provide a swing rotor for a centrifugal separator and a centrifugal separator which are capable of suppressing sliding resistance of a bucket during swinging, suppressing an increase in manufacturing cost to the minimum, and reducing regular maintenance, only by adding a simple machining process to the configuration according to the related-art.